Electrooptical transmission



A. w. KlsHPAUGl-l 1,707,486

ELCTROOPTICAL TRANSMISSION Filed April e, 192'? 2 sheets-sheet 1 @A QN um W mw. Nw v April 2, 1929.

April 2, 1929. A. w. KISHPAUGH ELECTROOPTICAL TRANSMISSION Filed April, 1927 2 Sheets-Sheet 2 S Lul Sv w w. Ny IN yArm/'wey Patented Apr. 2, 1929.

unirse STATES PATENT carica.

ARTHUR W. KISHPAUGH, OF EAST ORANGE, NEW JERSEY, ASSGNOR T0 BELL TELE- PHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION 0F NEW' YORK.

ELECTROOPTICAL TRANSMISSION.

Application filed April G, 1927. Serial No. 181,568.

This invention relates to electro-optical` transmission and more articularly to a televlsion or image producing system having means for controlling the average tone value y of'a produced image.

The present invent-ion provides an arrangement which is an improvement over the system disclosed in a copending application of Frank Gray, Serial No. 181,537, filed April 6, 1927. In the Gray system there is at the transmitting station a scanning device which comprises means for illuminating in rapid succession small elemental areas of the object, an image of which is to be produced at a receiving station. Light reflected from these elemental areas acts upon a light responsive device, such as a photo-electric cell, which serves to vary the amplitude of the unidirectional current flowing in the circuit in which the cell is connected. For light received by t-he cell from a certain stationary object, this varying uni-directional current may be analyzed into a steady direct current component and alternating current components of different `frequencies. The transmission-apparatus which is preferably of the type disclosed in a copending application of H. E. Ives and Frank Gray, Serial No. 181,511, filed April 6, 1927, is not capable of transmitting the steady direct current component and this apparatus also greatly attenuates the components of very loW frequency of the order of .10 cycles per second or less, so that currents of these frequencies are also practically lost in transmission. At the lreceiving station an oscillator is provided for generating high frequency current of the order of one million cycles per second upon which are impressed the currents incoming from the transmitting station, thereby producing a modulated high frequency current. This modulated high frequency current is impressed upon a light emitting device such as u glow discharge lamp having a plurality of spaced electrodes, these electrodes being connected to the source of modulated current through a commutating means which rotates in synchronism with the scanning device at the transmitting station. The position occupied by each electrode of the light emitting device corresponds-to the posltion occupied by a certain element-al area of the object, an image 'of Which is to be produced, so that age is to faithfully represent the object or l picture at the transmitting station, the amplitude of the unmodulated component must correspond to the steady direct current and very low frequency components which Were suppressed at the transmitting station. If the amplitude of the unmodulated component does not so correspond the average tone value of the produced image Will be either too light or too dark.

In accordance With this invention, lack of faithfulness in the produced image due to the suppression of low frequency currents by the transmission apparatus is corrected for at the receiving station by varying the amplitude of the unmodulated component of the high frequency oscillations, independently of the degree of modulation which is produced by the incoming picture currents. In the arrangement sclected for illustrating the invention a variable resistance is connected in series with the circuit supplying the direct current energy to the space current path of an electron discharge oscillator, the value of this resistance determining t-he amplitude of the unmodulated component of the high frequency energy.

A detailed description of an electro-optical system embodying this invention and of the theory which enters into its operation is given below, reference being made to the accompanying drawing in which:

Fig. 1 is a diagrammatic view of an electrooptical system showing one embodiment of the present invention.

Fig. 2 is a view partly in section of a portion of a glow discharge lamp employed at the receiving'station of this system, and

Fig. 3 is a diagrammaticvievv illustrating the theory of operation of the system.

Referring now particularly to Fig. l of the drawing, the light source is directed by the lenses 11 and 12 upon a small area on the scanning disc 13 which is revolved by the motor 14. The disc 13 is provided with numerous small apertures spirally arranged so that rays of light sweep over the areav of the opening in. screen 15 in `parallel lines, the

whole areabeing traversed in 1this manner during one complete revolution of the scanning disc 13. These light raysare bent in passing through the lens 16 and illuminate in rapid succession small elemental areas on the object .17. Good results have been obtained by providing fifty of these apertures in the disc 13 and rotating the disc at about 15 R. P. S. Under these conditions the Whole object is completely scanned in about 1/15 second or it is scanned by fifty successive parallel lines of light each requiring about 1/7 50 second to sweep across the object. Light reflected from the object 17 impinges upon a light sensitive device, such as photoelectric. cell 18. As the amount of light impinging upon the cell increases and decreases the voltage impressedy upon the amplifier 19 correspondingly increases and decreases.v

The amplifier is preferably of the type dis-v closed in the copending application of H. E. Ives and Frank Gray, supra, in which voltage variations produced by the pulsating current in the photo-electric cell are amplified, the steady directl current and low frequency components being suppressed. The alternating current components are impressed by transformer 20 upon the transmission ine 21. Both the transformer 20 and line 21 are adapted to transmit Waves Within a'wide band of frequencies from about 10 cycles' per second to 20,000 cycles er second. The transmission line 21 exten s to the receiving station Where it connects to the transformerr 22 which in turn is connected to the vacuum tube amplifier 23. The output circuit of this .amplifier is connected to an oscillator-modulator, described in detail hereinafter, which generates a high frequencycurrent, preferably ofthe order of a million cycles per second, and modulates this high frequency current with the picture currents received from Stoller and E.. R. Morton, Serial No. 200,799, filed June 23, 1927. Contact points ofthe the transmitting station. The modulated high frequency current leaves the oscillatormodulator through the conductors 24 and 25. Conductor 25 connects directly to a terminal 26 which connects to a common electrode 34 (shown in Fig. 2) of the light emitting device 27 While the conductor 24 connects to a brush 28 of commutator 29 which is driven by motor 30 in synchronism With thescanning disc 13 at the transmitting station. .A suitable synchronizing system is disclosed in a copend'ing `application of H. M.

commutatorl 29.y are connected to the terminal bank 31, the individual terminals of which gtures'in the scanning disc 13 at the transmitting station. rlhe ends of these tubes are connected so as to form a single unit'which is filled with an inert gas, such as neon, at low pressure. In Fig. 2 is shown a short section of one of these tubes Which comprises a glass cylinder 32, individual electrodes 33 of semicircular cross-section and secured to the outside of the cylinder, and the helical electrode 34 Which is common to the Whole light emitting device. Light emitted from the light emitting device impinges on a portion of a ground glass viewing screen 35 opposite one of the electrodes 33 to which Contact is made With the oscillator-modulator set through the commutator 28. The individual electrode which at a given instant of time is connectedto the oscillator-modulator set occupies a position with respect to other individual electrodes which corresponds to the elemental area of the object 17 being'scanned. It is thus apparent that an image of the object 17 appears on the viewing screen 35.

The oscillator-modulator set comprises the amplifier vacuum tube 36, the modulator vacuum tubes 37 and 38 the control electrodes of which are connected in parallel and the oscillator vacuum tubes 39 and 40, the control electrodes of which are also connected in parallel. connected to ground and the grounded generator 41 supplies space currentto the tube 36 through choke coil 42, to tubes 37 and 38 through low-frequency choke coil 43 and parasitic oscillation preventing choke coils 44 and 45, respectively, and to tubes 39 and 40 The cathodes 0f these tubes are through low frequency choke coil 46, variable resistance 47, high frequencyv choke coil 52, and the parasitic oscillation preventing choke coils 48 and 49, respectively. The anode of amplifier tube 36`is.coupled to the control electrodes of the modulator tubes 37 and 38 through the coupling vcondenser 50, and the anodes of the modulator tubes 37 and 38 are coupled to the anodes of the oscillator tubes 39 and 40 through choke coils 44 and- 45, respectivel coupling condenser. 51, high frequency c ioke coil 52 and the choke coils 48 and 49, respectively. The parasitic voscillation preventing choke coils 44, 45, 48 and 49 are designed to offer appreciable impedance only to frequencies above that Generated by the oscillator tubes 39 and 40, w iile the high frequency choke coil '5 2 offers a high impedance to this generated high frequency. The choke coils 42, 43 and 46 offer a high impedance to all of the frequency components of the picture current received ffrom'the transmitting station. The ano of the oscillator rents.

tubes 39 and 40 are connected to the tuning coil 53 through thechoke coils '48. and 49, respectively, and stopping condenser 54, and the control electrodes of these tubes are connected to the tuning coil through the grid condenser 55. The choke coil 56 and the high resistance 57 serve as a leak for the control electrodes of the oscillator tubes. The oscillator circuit is completed through the variable condenser 58 and 59, fixed condenser 60 and the resistance 61 which latter serves to broaden the tuning of this oscillatory cir; cuit. vIt is apparent that the operation of the oscillator-modulator is based upon the principle that the anode-cathode impedance of tubes. 37 and 38 is varied in accordance with the incoming picture currents and these impedance changes serve' to vary the shunt impedance between the anodes and cathodes of the oscillator tubes 39 and 4() or, in other words, these impedance changesl vary the anode-cathode potential of tubes 39 and 40 which impedance variations, in turn, cause the oscillator output current to be modulated in accordance with the incoming picture cur- The general type of oscillatormodulator is disclosed in vlleising Patent No. 1,559,870, issued November 3, 1925.

The variable resistance 47 which controls the direct current anode-cathode potential difference of the oscillator tubes 39 and 40 and therefore the value of the unmodulated component of the high frequency energy, serves to correct for the distortion in the image produced by the light emitting tube 27, because of changes in the average tone value due to the suppression by the transmission apparatus of the Zero and very low frequency components of the varying 'unidirectional current set up by the photoelectric cell 18. This will be made apparent by tracing the operation of the system with refence to the illustration given in Fig. 3. At A of this figure are represented two objects and (b) the transmission and image production of which are to be compared. The tone values of diiferent portions of these objects are designated by numerals to 74 as follows: 70, white; 71, light gray; 72, medium gray; 73, dark gray; and 74, black. At B, curves (a) and (b) respectively, represent` the varying unidirectional current which flows in the circuit in which the photoelectric cell 18 is connected in response to the light reflected from the objects (a) and (5) respectively, as the scanning beam traces one path across the objects in A, the paths being represented by the dotted traces. It will be noted that the current in the ycircuit is substantially zero when the black portions7 4 are being scanned, and a maximum current flows in the circuit when the white portions 70 are being scanned. Since steady currentcomponents of these current Waves are suppressed by the transmission apparatus as explained above, the Wave forms (a) and (b) at C having a zero steady current component are impressed upon the oscillatormodulator at the receiving station.

At D of Fig. 3, curves (a) and (b) show therelation between anode-cathode potential of the oscillator tubes and the peak value of output current of these tubes for high and low vvalue settings, respectively, of variable resistance 47. If this resistance is variedso that current variations corresponding to objects (a) and (b) operate on curves (a) and (b), respectively, at D, then the modulated high frequency output current of the oscillator-modulator or the E. M. F. impressed on the light emitting tube 27 will be represented by (a) and (b) ,-respcctively, at E of this ligure. The high frequency modulated current is impressed on the electrodes 33 and 34 of the light emitting device 27. The curve at F shows the relation between the voltage which is impressed across the electrodes of the light emitting device and the intensity of the light emitted therefrom. At G of Fig. 3 curves (a) and (b) represent the intensity of the light emitted by the elemental areas of tube 27 as thehigh frequency modulated waves (a) and (b), represented at E of Fig. 3, are impressed across the electrodes of the tube 27. If the numerals used at A of Fig. 3 are used to'represent the tone values of the image formed by these light variations, it is ap' parent that the images (a) and (Z2) at H of Fig: 3 correspond to the objects (a) and (b), respectively, shown at A of this ligure. It should be noted, if the current variations reprecented by (a) and(b) at C of Fig. 3 were employed to modulate the high frequency output current of theoscillator directly, that is, without changing the setting of resistance 47, that, in this case, the maximum and minimum values 90 and 91, respectively, of the modulated high frequency current as represented at E would be different for waves (a) and (b), respectively. This would cause a difference between the maximum and minimum values of light as represented by (a) and (b), respectively. at G of FigA 3. Since these peak values of light intensity correspond to white and black, respectively, of the objects (a) and (b) at A, it is obvious that, if

these peak values are not equal, the portion 70 of the image (a) at H will have a tone value dierent from that of portion 70 or image (b) at H. So also there will be a 'difference between the tone value corresponding to the black portions 74 and other portions of these objects. It is apparent, therefore, that the resistance 47 may be varied in accordance with changes in the substantially steady component of the unidirectional varying current set up by the photoelectric cell 18 and thereby correct the distortion of the .average tone value of the produced image due to the suppression by the transmission medium of the zero and very low frequency components of the varying unidirectional current just referred to. It is apparent, moreover, that a battery having a variable connection thereto or other means may be substituted for the variable resistance 47 in order to increase or decrease the amplitude of the high frequency current output of the oscillator.

What is claimed is:

l, The combination with an energy responsive element actuated by oscillatory energy, of an oscillator for actuating said element, means to modulate the oscillations applied from said oscillator to said element, and means to vary the unmodulated component of the applied oscillations independently of the modulated component to control the character of the response of said elevsignal variations, 'and means to control the mean amplitude ofthe oscillatory energy applied to said lamp, independently of the amplitude variations thereof, to determine the average tone of a' produced image.

3. In a. television or image producing system, a source of energy having variations characteristic of an image to be produced, translating means for producing an image under the control of energy from said source,

an electric discharge device having a ,cathy ode and an anode included in said translating means, and means to change the direct current potential impressed on said anode and cathode to control the average tone I value of the produced image.

4. In a televislon or image producing system, a source of energy having variations characteristic of an image to be produced, translating means for producing an image under the control of energy from said source, a plurality of electric discharge devices included in said translating device each hav ing an anode, a cathode and an impedance controlling element, means connected between the anode and cathode of one of said devices to control the average tone value of I the produced image, and means connected between the impedance controlling element and the cathode of another ofA said `devices for controlling the difference between the maximum and minimum tone Values of elemental areas of said image.

5. In an electro-optical transmission system, a source of current having variations characteristlc of tone changes of elemental areas of an ob'ect, an image of which is to be produced, means to modulate an alternating current in accordance with -varying current from said source, a translating device for translatin said modulated current into light of varying intensity, and means to .change the amplitude of the unmodulated sponsive to amplitude variations thereof,

means for modulating saidhigh frequency alternating current with an alternating'current component of said varying uni-direc tional current, and means for changing the amplitude of the unmodulated component of said modulated high frequency alternat` ing current independently of the modulated component lto compensate for changes in the substantially steady current component of said varying uni-directional current.

7. In combination, a source of varying uni-directional current, a vacuum tube oscillator for generating a high frequency alternating current, said oscillator comprising a .vacuum tube having an anode, a cathodeY and a control electrode,I means for utilizing said high. frequency current'and responsive to amplitude variations thereof, means for modulating said high-frequency alternating current by varying the anode-cathode potentla-l of said l,vacuum tube in accordance with an alternating current component ofy said varying uni-directional current', and means for varying the amplitude of the unmodulated component of said modulated alternating current independently o'f the modulated component to compensate for changes in the substantially steady current component of said varying uni-directional current.

8. In an electro-optical transmission system, a source of light of varying intensity, means for converting said light variations into current of varying amplitude, a source of -high frequency current, a device utilizing said high frequency current for emitting light which varies in intensity in accordance with the amplitude variations 'of said high frequency current, means for modulating said high frequency current with the varying current which corresponds to the light intensity Variations of said source, and'means for increasing or decreasing the amplitude of the unmodulated component of said modulated high frequency current independently of the modulated component as-the average intensity of the light from said source increases or decreases, respectively.

1,707,486l y a 5 which said modulated high frequency curvarying the energizingl potential supplied to rent is impressed for emitting light Which the oscillator of sai oscillator-modulator varies in intensity in accordance with the set in order to correct the average tone value amplitude variations of 'said high frequency of said image for the distortion ue to the modulated current, and means 'for varying suppression by said transmission medium of the amplitude of the unmodulated component the steady componentof the varying uni-.di-

of said modulated high frequency current inrectional current set up at said transmitting dependently of the modulated component to station. compensate for changes in the substantially 1l. ln a 'television or image producing i Steady current com onent of said uni-direcsystem, a source of current having variations i5 given o by said light source.

tional current, there y causing chan-ges in the characteristic of an image to beproduced, average intensity of the light given oi by an oscillator including an electric discharge said light emitting means to corres ond With device havin a cathode, an anode and aconchanges in the average intensity o the light trol electro e for generating a highfrequency current, a second electric discharge 10. An electro-optical transmission sysdevice havin an input and an output cirtem, comprising a transmitting station and cuit connecte ,respectively, to said source of a receiving station` a circuit including-a light current and to the anode-cathode circuit o sensitive device at said transmitting station said first mentioned electric discharge 2o for setting up varying uni-directional curvice for varying the anode-cathode potential rent in said circuit in accordance With the nof said first mentioned electric discharge detensity variations ofl the light reflected from vicel and for modulating said high frequency a'nobject an image of which is to be produced current with current from said source, a at said receiving station, a transmission 'melight emitting device actuated by said high dium, cap-able of transmitting alternating frequency modulated current for producing Y current only, connecting said transmitting said image, a source f steady potential conand receiving stations,- an oscillator-modulanected in the anode-cathode circuit of the tor set at said receiving station connected first mentioned electric discharge device, to said transmission medium for producing.: and means'connected in said anode-cathode a high frequency current modulated with circuitfor varying said steady potential and said incoming alternating current, a source of. thereby vary the average tone value of the energizing potential for said oscillator, modimage produced.

i ulator set, a light emitting device connected r In witness whereof, I hereunto subscribe to said oscillator-modulatorl set for, producmy name this 6th day oi April A. D., 1927.

ing an image of said object, andv means for ARTHUR W. KISHPAUGH. l 

